On a farm, some of the cows that calve go down in the first days and get up again with a calcium injection. A few weeks later some develop ketosis, and one or two a displaced abomasum. The farmer puts it down to bad luck. Looking at the records, though, these problems all cluster in the same period, the first month after calving, and almost all of them occur in cows fed the same ration in the dry period.
Why is it so critical?
The three weeks before calving and the three weeks after are the hardest period in a cow's life. With calving, milk production starts and the need for calcium, energy and protein multiplies within days. Yet the cow's feed intake drops in the days before calving and rises only slowly over the weeks after. That gap between need and intake is the root cause of milk fever, ketosis and the problems that follow them.
Milk fever and the cation-anion balance
The calcium that goes into milk at calving lowers blood calcium quickly. If the cow's mechanism for releasing calcium from bone cannot keep up with this sudden need, blood calcium falls below a critical level. Clinical milk fever shows as a cow that goes down, but what is really common is subclinical hypocalcaemia, which shows no signs and quietly weakens the cow's appetite, rumen movement and immunity.
The cation-anion difference of the ration before calving has a direct effect on how ready that mechanism is. When the ration is high in potassium and sodium, the cow's blood becomes slightly alkaline and the hormones that release calcium work less well. Making the ration slightly acidic with anionic salts or sources rich in chloride and sulphur sets the mechanism going before calving.
Take an example, with illustrative numbers. A close-up ration with 0.10 percent sodium, 1.40 percent potassium, 0.40 percent chloride and 0.25 percent sulphur on a dry matter basis has a cation-anion difference of about +134 mEq/kg of dry matter by the commonly used equation. That value sends the cow into calving in an alkaline state. Most of the difference comes from potassium, and the largest source of potassium is usually forage. Using a low-potassium straw or corn silage instead of a high-potassium alfalfa cuts the need for anionic salts considerably.
Anionic salts are unpalatable and can lower intake. So the right order is to lower the ration's cation load first through the choice of forage, then add only as much anionic salt as needed. Whether it is working is followed by measuring the cows' urine pH regularly. The target range depends on the programme used and should be set together with the vet.
The energy gap and ketosis
After calving, the cow covers the energy she cannot get from feed by drawing on body fat. That is normal, but when fat is mobilised too fast and in too great an amount, the liver cannot cope. Fat builds up in the liver and ketone bodies rise. Ketosis lowers both milk yield and fertility and raises the risk of a displaced abomasum.
The strongest risk factor for ketosis is a cow that is over-conditioned at calving. A cow that gets fat in the dry period eats less before and after calving and uses her body fat faster. So a cow's condition should be adjusted at the end of lactation, before she is dried off. In the dry period the aim is to hold condition, not to put weight on or take it off.
The first weeks after calving
After calving, the aim of the ration is to raise feed intake as fast as possible. For that, the ration needs to be palatable, fresh and always in the bunk. Keeping fresh cows apart from the dominant animals in the herd, in a group with enough bunk space, raises intake. Because sudden exposure to high starch at the move from dry to lactation ration raises the risk of acidosis, feeding small amounts of the lactation ingredients in the weeks before calving prepares the rumen.
Watching closely what the cow eats, how much milk she gives and how healthy she is in the first days after calving is the most effective way to catch problems early. A cow whose intake rises more slowly than expected is often giving the first sign of a problem.
Following body condition
Body condition score is the cheapest and most useful tool in transition management. Scoring cows at dry-off, at calving and in the first weeks after calving shows which cows are at risk. Cows that lose more than one point of condition in the first month after calving show that the energy gap has grown too large and that the risk of ketosis is high. Spotting these cows early buys time for both treatment and a ration correction.
Rations by group
The basis of transition management is to feed dry cows not as one group but as at least two: cows early in the dry period and cows three weeks from calving. A separate group and ration for fresh cows also makes a big difference in high-yielding herds.
OptiFormula TMR calculates requirements for dry and lactating cows with models such as NASEM 2021 and lets you prepare a separate ration for each group of animals. Because forage analyses are kept together with the feed library, you can see while building the dry cow ration which forage is adding to the potassium load. A mixer wagon loading list is prepared from the approved ration, so different rations for different groups are applied without mix-ups.
The transition period is short, but its effect is felt through the whole lactation. Care taken over the three weeks before calving shows up directly in the next ten months of milk yield, fertility and vet bills.
